Mixing
Radial Velocity Clarification Sought
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According to Google, radial velocity is "the velocity of a star or other body along the line of sight of an observer".
The radial velocity of Sirius according to Google is −5.50 km/s.
If the number is positive, does that mean it's moving away or towards us?
radial-velocity
edited Aug 19 at 6:40
SergiusPro
1943
asked Aug 18 at 9:16
MiscellaneousUser
409211
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up vote
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According to Google, radial velocity is "the velocity of a star or other body along the line of sight of an observer".
The radial velocity of Sirius according to Google is −5.50 km/s.
If the number is positive, does that mean it's moving away or towards us?
radial-velocity
edited Aug 19 at 6:40
SergiusPro
1943
asked Aug 18 at 9:16
MiscellaneousUser
409211
Negative velocity means it's moving closer to us, see astronomy.stackexchange.com/questions/11893/…
– barrycarter
Aug 18 at 13:45
add a comment |Â
up vote
4
down vote
favorite
up vote
4
down vote
favorite
According to Google, radial velocity is "the velocity of a star or other body along the line of sight of an observer".
The radial velocity of Sirius according to Google is −5.50 km/s.
If the number is positive, does that mean it's moving away or towards us?
radial-velocity
edited Aug 19 at 6:40
SergiusPro
1943
asked Aug 18 at 9:16
MiscellaneousUser
409211
According to Google, radial velocity is "the velocity of a star or other body along the line of sight of an observer".
The radial velocity of Sirius according to Google is −5.50 km/s.
If the number is positive, does that mean it's moving away or towards us?
radial-velocity
edited Aug 19 at 6:40
SergiusPro
1943
asked Aug 18 at 9:16
MiscellaneousUser
409211
edited Aug 19 at 6:40
SergiusPro
1943
edited Aug 19 at 6:40
SergiusPro
1943
edited Aug 19 at 6:40
SergiusPro
1943
1943
asked Aug 18 at 9:16
MiscellaneousUser
409211
asked Aug 18 at 9:16
MiscellaneousUser
409211
asked Aug 18 at 9:16
MiscellaneousUser
409211
409211
Negative velocity means it's moving closer to us, see astronomy.stackexchange.com/questions/11893/…
– barrycarter
Aug 18 at 13:45
add a comment |Â
Negative velocity means it's moving closer to us, see astronomy.stackexchange.com/questions/11893/…
– barrycarter
Aug 18 at 13:45
Negative velocity means it's moving closer to us, see astronomy.stackexchange.com/questions/11893/…
– barrycarter
Aug 18 at 13:45
Negative velocity means it's moving closer to us, see astronomy.stackexchange.com/questions/11893/…
– barrycarter
Aug 18 at 13:45
add a comment |Â
2 Answers
2
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oldest
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up vote
2
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accepted
The number -5.5 km/s in this context means that the relative line of sight velocity between Sirius and the Sun is 5.5 km/s in the sense that Sirius and the Sun are getting closer to each other.
Note that the line of sight velocity of Sirius as observed from the Earth will vary throughout the year, since the Earth moves with an orbital speed of 30 km/s around the Sun. Astronomical radial velocities that are quoted in catalogues will almost certainly be corrected for this and will be referred to as "heliocentric radial velocities" if corrected to the Sun;s reference frame, or "barycentric radial velocities" if corrected to the centre of mass of the solar system (which is almost the same to within 10 m/s or so).
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
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up vote
4
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If you are referring to the Earth...
If the number is positive, the star is moving away from us. When the number is negative, the star is moving towards us.
Hope that helps!
Source with more info: https://cseligman.com/text/stars/radialvelocity.htm
answered Aug 18 at 15:35
MystaryPi
13811
What do you mean by "us"? If you mean the Earth, then the answer is incorrect
– Rob Jeffries
Aug 19 at 6:34
I used the word us in the original question so I guess he was following suit. Your point below is noted.
– MiscellaneousUser
Aug 19 at 11:48
Hmm... Makes sense. Thanks for pointing it out!
– MystaryPi
Aug 19 at 15:03
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
The number -5.5 km/s in this context means that the relative line of sight velocity between Sirius and the Sun is 5.5 km/s in the sense that Sirius and the Sun are getting closer to each other.
Note that the line of sight velocity of Sirius as observed from the Earth will vary throughout the year, since the Earth moves with an orbital speed of 30 km/s around the Sun. Astronomical radial velocities that are quoted in catalogues will almost certainly be corrected for this and will be referred to as "heliocentric radial velocities" if corrected to the Sun;s reference frame, or "barycentric radial velocities" if corrected to the centre of mass of the solar system (which is almost the same to within 10 m/s or so).
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
add a comment |Â
up vote
2
down vote
accepted
The number -5.5 km/s in this context means that the relative line of sight velocity between Sirius and the Sun is 5.5 km/s in the sense that Sirius and the Sun are getting closer to each other.
Note that the line of sight velocity of Sirius as observed from the Earth will vary throughout the year, since the Earth moves with an orbital speed of 30 km/s around the Sun. Astronomical radial velocities that are quoted in catalogues will almost certainly be corrected for this and will be referred to as "heliocentric radial velocities" if corrected to the Sun;s reference frame, or "barycentric radial velocities" if corrected to the centre of mass of the solar system (which is almost the same to within 10 m/s or so).
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
add a comment |Â
up vote
2
down vote
accepted
up vote
2
down vote
accepted
The number -5.5 km/s in this context means that the relative line of sight velocity between Sirius and the Sun is 5.5 km/s in the sense that Sirius and the Sun are getting closer to each other.
Note that the line of sight velocity of Sirius as observed from the Earth will vary throughout the year, since the Earth moves with an orbital speed of 30 km/s around the Sun. Astronomical radial velocities that are quoted in catalogues will almost certainly be corrected for this and will be referred to as "heliocentric radial velocities" if corrected to the Sun;s reference frame, or "barycentric radial velocities" if corrected to the centre of mass of the solar system (which is almost the same to within 10 m/s or so).
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
The number -5.5 km/s in this context means that the relative line of sight velocity between Sirius and the Sun is 5.5 km/s in the sense that Sirius and the Sun are getting closer to each other.
Note that the line of sight velocity of Sirius as observed from the Earth will vary throughout the year, since the Earth moves with an orbital speed of 30 km/s around the Sun. Astronomical radial velocities that are quoted in catalogues will almost certainly be corrected for this and will be referred to as "heliocentric radial velocities" if corrected to the Sun;s reference frame, or "barycentric radial velocities" if corrected to the centre of mass of the solar system (which is almost the same to within 10 m/s or so).
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
answered Aug 18 at 16:39
Rob Jeffries
47.1k490144
47.1k490144
add a comment |Â
add a comment |Â
up vote
4
down vote
If you are referring to the Earth...
If the number is positive, the star is moving away from us. When the number is negative, the star is moving towards us.
Hope that helps!
Source with more info: https://cseligman.com/text/stars/radialvelocity.htm
answered Aug 18 at 15:35
MystaryPi
13811
What do you mean by "us"? If you mean the Earth, then the answer is incorrect
– Rob Jeffries
Aug 19 at 6:34
I used the word us in the original question so I guess he was following suit. Your point below is noted.
– MiscellaneousUser
Aug 19 at 11:48
Hmm... Makes sense. Thanks for pointing it out!
– MystaryPi
Aug 19 at 15:03
add a comment |Â
up vote
4
down vote
If you are referring to the Earth...
If the number is positive, the star is moving away from us. When the number is negative, the star is moving towards us.
Hope that helps!
Source with more info: https://cseligman.com/text/stars/radialvelocity.htm
answered Aug 18 at 15:35
MystaryPi
13811
What do you mean by "us"? If you mean the Earth, then the answer is incorrect
– Rob Jeffries
Aug 19 at 6:34
I used the word us in the original question so I guess he was following suit. Your point below is noted.
– MiscellaneousUser
Aug 19 at 11:48
Hmm... Makes sense. Thanks for pointing it out!
– MystaryPi
Aug 19 at 15:03
add a comment |Â
up vote
4
down vote
up vote
4
down vote
If you are referring to the Earth...
If the number is positive, the star is moving away from us. When the number is negative, the star is moving towards us.
Hope that helps!
Source with more info: https://cseligman.com/text/stars/radialvelocity.htm
answered Aug 18 at 15:35
MystaryPi
13811
If you are referring to the Earth...
If the number is positive, the star is moving away from us. When the number is negative, the star is moving towards us.
Hope that helps!
Source with more info: https://cseligman.com/text/stars/radialvelocity.htm
answered Aug 18 at 15:35
MystaryPi
13811
edited Aug 19 at 15:04
answered Aug 18 at 15:35
MystaryPi
13811
answered Aug 18 at 15:35
MystaryPi
13811
answered Aug 18 at 15:35
MystaryPi
13811
13811
What do you mean by "us"? If you mean the Earth, then the answer is incorrect
– Rob Jeffries
Aug 19 at 6:34
I used the word us in the original question so I guess he was following suit. Your point below is noted.
– MiscellaneousUser
Aug 19 at 11:48
Hmm... Makes sense. Thanks for pointing it out!
– MystaryPi
Aug 19 at 15:03
add a comment |Â
What do you mean by "us"? If you mean the Earth, then the answer is incorrect
– Rob Jeffries
Aug 19 at 6:34
I used the word us in the original question so I guess he was following suit. Your point below is noted.
– MiscellaneousUser
Aug 19 at 11:48
Hmm... Makes sense. Thanks for pointing it out!
– MystaryPi
Aug 19 at 15:03
What do you mean by "us"? If you mean the Earth, then the answer is incorrect
– Rob Jeffries
Aug 19 at 6:34
What do you mean by "us"? If you mean the Earth, then the answer is incorrect
– Rob Jeffries
Aug 19 at 6:34
I used the word us in the original question so I guess he was following suit. Your point below is noted.
– MiscellaneousUser
Aug 19 at 11:48
I used the word us in the original question so I guess he was following suit. Your point below is noted.
– MiscellaneousUser
Aug 19 at 11:48
Hmm... Makes sense. Thanks for pointing it out!
– MystaryPi
Aug 19 at 15:03
Hmm... Makes sense. Thanks for pointing it out!
– MystaryPi
Aug 19 at 15:03
add a comment |Â
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Negative velocity means it's moving closer to us, see astronomy.stackexchange.com/questions/11893/…
– barrycarter
Aug 18 at 13:45